Weaker security in arrivals

The international arrivals hall is an area with weaknesses the attackers may have exploited, CNN's Senior International Correspondent Clarissa Ward reports.

"There's heavy security at the entrance to the international departures hall," Ward said. "There's a full screening process. You have an X-ray machine and you have to go through a metal detector. But in the arrivals hall, of course you don't have that same level of security, so two of the attackers we believe went into the arrival halls."

People going to the arrivals section on the bottom floor are required to go through metal detectors but are overseen only by a light guard presence.

The third bomber meanwhile detonated at the car park, outside the first X-ray security screening point. It's unclear whether the attacker's original intent was to set off an explosion there but it raises another issue in airport security.

Authorities can create and bolster checks that prevent 9/11 style attacks where terrorists board and take control of planes, but attackers can adjust their targets to areas before the screening process begins.

Bob Baer, a former CIA intelligence officer who specializes in Middle East security issues, said there is no foolproof way to preventing a similar airport attack.

"You cannot protect these airports 100% ... especially in a place like Turkey, where ISIS has cells everywhere," he said.

Security staff response

What about the response from Turkish airport security as the tragedy unfolded?

Harrowing surveillance footage shows what appears to be a Turkish security personnel officer shooting one of the attackers. The attacker falls to the ground and drops a gun that slides across the floor. The personnel approaches but seeming to realize the imminent danger, runs away just seconds before the attacker detonates.

Istanbul Ataturk Airport

-- 11th busiest airport in the world (2015)

-- Europe's third busiest airport (2015)

-- ~62 million passengers passed last year

-- There are two main passenger terminals

-- Terminal 1: older, smaller, domestic

-- Terminal 2: newer, bigger, international

-- Vehicle checkpoint at compound entrance

-- X-ray checkpoint at terminal entrance

-- The airport is roughly 15 miles from the city

Source: Airports Council International/CNN

Witnesses said the response to the threat seemed swift.

As the attack was ongoing and it was unclear how many bombers there were, security staff escorted people deeper inside the airport to the gates, past the second X-ray scan point, where they would be safer.